1. Field of the Invention
The present invention relates to improvements of an apparatus for automatically measuring a blood pressure of a living subject.
2. Related Art Statement
There is known an oscillometric-type automatic blood-pressure measuring apparatus which automatically measures a blood pressure of a living subject according to an oscillometric method. The oscillometric-type automatic blood-pressure measuring apparatus includes an inflatable cuff which is adapted to be wound around a prescribed portion of the subject, obtains a cuff pulse wave occurring to the cuff while a pressing pressure of the cuff is slowly changed, and determines a blood pressure of the subject based on the change of respective amplitudes of respective heartbeat-synchronous pulses of the cuff pulse wave.
However, the above automatic blood-pressure measuring apparatus may measure an erroneous blood pressure of the subject, because of a physical motion of the subject during the blood-pressure measuring operation, occurrence of an arrhythmic pulse to the cuff, or noise produced by its peripheral devices. Hence, a blood-pressure measuring apparatus disclosed in Japanese Patent Document No. 2-25610 displays an array of respective amplitudes of respective heartbeat-synchronous pulses, arranged in an order of occurrence of the pulses, in a two-dimensional graph defined by a first axis indicative of pressing pressure of cuff as a first parameter and a second axis indicative of amplitude of cuff pulse wave as a second parameter, so that a degree of reliability of measured blood pressure may be judged by an operator. From the array of amplitudes being displayed, it is possible to observe a magnitude of each of the amplitudes or the manner of distribution of the amplitudes, and thereby judge the reliability of measured blood pressure. If it is judged from the displayed array of amplitudes that the reliability of measured blood pressure is insufficient, the blood-pressure measuring apparatus may be operated again to carry out another blood-pressure measuring operation and thereby obtain a reliable blood pressure.
The above-described conventional automatic blood-pressure measuring apparatus may be used in those cases in which a physical condition of a patient may abruptly change during, e.g., a surgical operation. If the condition of the patient abruptly changes, it is needed to obtain a reliable blood pressure of the patient, as soon as possible, so as to administer an appropriate treatment to the patient. However, the conventional automatic blood-pressure measuring apparatus cannot enable an operator to find an abnormality of a blood-pressure measuring operation, before the blood-pressure measuring operation is finished. Thus, there has been a demand for such an automatic blood-pressure measuring apparatus which can enable an operator to more quickly find an abnormality of a blood-pressure measuring operation.
It is therefore an object of the present invention to provide an automatic blood-pressure measuring apparatus which can enable an operator to quickly judge an abnormality of a blood-pressure measuring operation.
The Inventor has carried out extensive studies to achieve the above object, and has found the following fact: Since, in the oscillometric blood-pressure measuring method, a blood pressure is determined based on the change of respective amplitudes of respective heartbeat-synchronous pulses of a cuff pulse wave, it is possible for an operator to find an abnormality of a blood-pressure measuring operation, during that measuring operation, if each of the amplitudes of the cuff pulse wave is successively displayed during the measuring operation so that the change of the amplitudes may be observed by the operator.
Meanwhile, an automatic blood-pressure measuring apparatus disclosed in Japanese Patent Document No. 11-4813 has the function of successively displaying, during a blood-pressure measuring operation, each of respective amplitudes of respective heartbeat-synchronous pulses of a cuff pulse wave that are obtained in the measuring operation. However, this apparatus displays the amplitude of only each one heartbeat-synchronous pulse of the cuff pulse wave. Therefore, it is difficult for an operator to judge whether that amplitude is normal, or is caused by an arrhythmic pulse, or by noise produced by physical motion.
The above object has been achieved by the present invention. According to the present invention, there is provided an apparatus for automatically measuring a blood pressure of a living subject, comprising an inflatable cuff which is adapted to be wound around a portion of the subject, a cuff pulse wave including a plurality of heartbeat-synchronous pulses occurring to the cuff while a pressure in the cuff is changed; a blood-pressure determining means for determining a blood pressure of the subject based on a change of respective amplitudes of the heartbeat-synchronous pulses of the cuff pulse wave; a display device which has a two-dimensional screen consisting of a plurality of picture elements; and an amplitude displaying means for successively displaying, on the two-dimensional screen of the display device and while the pressure of the cuff is changed, the amplitude of each of the heartbeat-synchronous pulses of the cuff pulse wave, such that the amplitude of the each heartbeat-synchronous pulse of the cuff pulse wave is comparable with at least one prior amplitude of at least one prior heartbeat-synchronous pulse of the cuff pulse wave that is prior to the each heartbeat-synchronous pulse.
According to the present invention, the amplitude displaying means successively displays, on the display device and while the pressure of the cuff is changed, the amplitude of each pulse of the cuff pulse wave that is successively obtained, such that the amplitude of the each pulse of the cuff pulse wave is comparable with a prior amplitude of a prior pulse of the cuff pulse wave. If the current blood-pressure measuring operation is normal, the respective amplitudes of respective pulses of the cuff pulse wave should monotonously increase till the greatest amplitude is detected; and after the greatest amplitude is detected, the respective amplitudes of respective pulses of the cuff pulse wave should monotonously decrease. Therefore, when an operator observes that the amplitude of each pulse of the cuff pulse wave, successively displayed on the display device, has not normally changed from the amplitude of the prior pulse of the cuff pulse wave, the operator can judge, at that timing, that the current blood-pressure measuring operation is abnormal.
According to a preferred feature of the present invention, the apparatus further comprises a memory device which stores respective amplitudes of a past series of heartbeat-synchronous pulses of the cuff pulse wave that are successively obtained in a past blood-pressure measuring operation; a reference-amplitude determining means for determining a reference amplitude, based on the respective amplitudes of the heartbeat-synchronous pulses of the past series stored in the memory device; and an amplitude normalizing means for successively normalizing, based on the reference amplitude determined by the reference-amplitude determining means, the amplitude of the each of the heartbeat-synchronous pulses that are successively obtained in a current blood-pressure measuring operation, into a normalized amplitude of the each heartbeat-synchronous pulse, and the amplitude displaying means successively displays, on the two-dimensional screen of the display device and while the pressure of the cuff is changed in the current blood-pressure measuring operation, the normalized amplitudes of the each of the heartbeat-synchronous pulses, such that the normalized amplitude of the each heartbeat-synchronous pulse is comparable with at least one prior normalized amplitude of the at least one prior heartbeat-synchronous pulse prior to the each heartbeat-synchronous pulse.
In the case where an amplitude of each pulse of a cuff pulse wave that is successively obtained in a blood-pressure measuring operation is normalized, and displayed, based on an amplitude of a different pulse of the cuff pulse wave obtained in the measuring operation, for example, in the case where an amplitude of each current pulse of a cuff pulse wave is displayed with a constant magnitude by normalizing, and displaying, an amplitude of the last pulse of the cuff pulse wave based on the amplitude of the current pulse, it is difficult for an operator to judge whether each pulse of the cuff pulse wave successively obtained in the blood-pressure measuring operation is too weak to use to determine a reliable blood pressure. In contrast, according to this feature, the reference-amplitude determining means determines the reference amplitude based on the amplitudes of the past pulses, and the amplitude normalizing means successively normalizes, based on the reference amplitude, the amplitude of the each pulse successively obtained, into a normalized amplitude. And, the amplitude displaying means successively displays, on the display device, the normalized amplitude of the each pulse, such that the normalized amplitude of the each is comparable with the prior normalized amplitude of the prior pulse. Thus, the operator can easily judge whether each pulse of the cuff pulse wave successively obtained in a blood-pressure measuring operation is too small to use to determine a reliable blood pressure.
According to another preferred feature of the present invention, the apparatus further comprising a memory device which stores respective amplitudes of a past series of heartbeat-synchronous pulses of the cuff pulse wave that are successively obtained in a past blood-pressure measuring operation, such that an array of the respective amplitudes of the heartbeat-synchronous pulses of the past series can be arranged in an order of occurrence thereof to the cuff in the past blood-pressure measuring operation; and an amplitude-array displaying means for displaying, on the two-dimensional screen of the display device and while the pressure of the cuff is changed in a current blood-pressure measuring operation, the array of the respective amplitudes of the heartbeat-synchronous pulses of the past series, such that the amplitude of the each of the heartbeat-synchronous pulses of the cuff pulse wave that is successively displayed on the display device by the amplitude displaying means in the current blood-pressure measuring operation is comparable with the array of the respective amplitudes of the heartbeat-synchronous pulses of the past series that is arranged in the order of occurrence.
According to this feature, the amplitude-array displaying means displays the array of amplitudes obtained in the past blood-pressure measuring operation, such that the amplitude of each pulse of the cuff pulse wave that is successively displayed is comparable with the array of amplitudes arranged in the order of occurrence thereof. Therefore, in the case where the array of amplitudes displayed is an array of amplitudes used to provide a correct blood pressure, the operator can easily compare the amplitude of each pulse of the cuff pulse wave that is successively displayed in the current blood-pressure measuring operation, with that array of amplitudes, and judge that the current blood-pressure measuring operation is abnormal at the first time when the operator recognizes that the tendency of change of the amplitude of each pulse of the cuff pulse wave largely differs from the tendency of change of the past array of amplitudes.
According to another preferred feature, the amplitude displaying means successively displays, while the pressure of the cuff is changed, the amplitude of the each of the heartbeat-synchronous pulses of the cuff pulse wave, and the at least one prior amplitude of the at least one prior heartbeat-synchronous pulse of the cuff pulse wave, in a two-dimensional graph which is displayed on the two-dimensional screen of the display device and which is defined by a cuff-pressure axis indicative of cuff pressure as a first parameter and an amplitude axis indicative of amplitude of cuff pulse wave as a second parameter, and the apparatus further comprises a blood-pressure-symbol displaying means for displaying, when the blood pressure of the subject is determined by the blood-pressure determining means, a blood-pressure symbol indicating the thus determined blood pressure, in a vicinity of the cuff-pressure axis of the two-dimensional graph.
According to this feature, the operator can easily judge whether the current blood-pressure measuring operation is abnormal, by comparing the blood-pressure symbol with the tendency of change of the amplitudes of the cuff pulse wave.